The application of video display monitors in such diverse areas as finance, design, graphic arts and manufacturing has undergone an explosive surge in growth. This growth corresponds to the depth that personal computers and other microprocessor controlled devices have penetrated business and personal use. The requirements of monitors addressing the myriad of diverse applications in today's market extend well beyond the capabilities of the television receivers designed for commercial broadcast reception. These monitor applications individually engender a subset of system requirements specific to each application, and further, individual applications often represent small niches in an otherwise large monitor market. Taken together, these two attributes have forced a degree of monitor customization by manufacturers with the attendant high cost and price associated with custom manufacturing operations.
An example of this problem resides in the market for engineering work stations. These specialized computer systems often mandate a level of monitor performance beyond commercially established standards. A computer aided design/computer aided manufacturing (CAD/CAM) work station directed to semi-conductor circuit design will invariably require a high resolution display monitor for the presentation of closely arrayed thin circuit lines to the user or designer. The high resolution display is required to accurately present the line information while minimizing the staircase effect associated with the horizontal scanning process.
Other work station applications will focus on different display attributes, such as color richness. The available color palette is of critical importance to the graphic designer developing color graphics for, e.g., the product packaging industry. Again, the capability to provide rich color images resides in the specific control circuitry of the display monitor.
Display monitors have also found extended use in applications requiring real time monitoring of multiple incoming video signals wherein these incoming signals may represent various and differing video format standards. An example of this application is found in the command and control operations for military installations. A single monitor must quickly shift between disparate incoming video signals to provide the observer a real time, accurate display. These incoming signals will include local broadcasts using the NTSC broadcast format, and foreign broadcasts in PAL, SECAM, or other video format corresponding to the locale of the broadcast.
A common thread seen in these applications is the need to provide a high resolution monitor capable of some customization to the requirements of specific end users while simultaneously addressing specific industry video standards, such as EGA, VGA, etc. and broadcast standards, i.e., NTSC, PAL and SECAM. These established formats vary from each other in the timing signals associated with the delivery of the video and audio information. Image timing refers to the horizontal scanning rate and vertical frame rate associated with the raster scan across the display screen. These rate values are the synchronization signals that control the placement of picture information in the image.
Monitor performance is a function of the timing of the video format, in terms of horizontal and vertical synchronization. Indeed, the image resolution is directly proportional to the horizontal line scanning frequency, which will vary depending on the video format (e.g., 15.750 kHz for NTSC broadcast format). Display monitors are normally considered high resolution if the horizontal scanning rate exceeds twice the NTSC standard, or about 31.5 kHz, although resolution can also be increased by lowering the vertical frame rate, e.g., from 60 Hz to 43 Hz. Lowering the vertical frame rate is limited by the appearance of a user detectable flicker on the monitor screen at the lower frame frequencies.
Prior efforts to provide multiple timing capabilities in display monitors has for the most part been extremely limited. For example, in U.S. Pat. No. 4,679,091 (to Kikuchi et al., the contents of which are herein incorporated by reference as if restated in full), the monitor switches the duty cycle of the horizontal oscillator in response to certain higher frequency scan rates. This system on the other hand is limited to scan rates about double of the NTSC video format. A similarly restricted system is provided in U.S. Pat. No. 4,684,987 (to Tsutsui, the contents of which are herein incorporated by reference as if restated in full).
The requirements of many of the important monitor applications involve horizontal line scanning rates that can extend up to 75 kHz, and different so-called standards are appearing with timing formats in between the NTSC format and these higher values. The industry has, therefore, long sought a display monitor capable of displaying a range of video formats while simultaneously providing the user the ability to customize the display monitor to specific non-standard video formats.
It was with this understanding of the needs of the display monitor marketplace that the present invention was developed.